1. Field of the Invention
The present invention relates to an electric generation control system for use on a hybrid vehicle having a propulsive electric motor energizable by a battery and an electric generator actuated by an internal combustion engine for energizing the propulsive electric motor.
2. Description of the Related Art
Growing concern in recent years over environmental protection has led to various efforts to develop for practical applications electric vehicles which have a propulsive electric motor energizable by a battery to transmit drive forces to drive wheels for propelling the electric vehicle. One of the important requirements for such electric vehicles to satisfy is that the range which they can travel without recharging the battery be maximized and the discharging of the battery be minimized for increased battery service life.
One solution disclosed in Japanese laid-open patent publication No. 4-29504 is a hybrid vehicle carrying an electric energy generating apparatus having an electric generator and an internal combustion engine for actuating the electric generator. Electric energy generated by the electric generator is supplied to charge a battery or to energize a propulsive electric motor.
While the disclosed hybrid vehicle is running, the battery energizes the electric generator to operate as an electric motor in a motor mode to start the engine. After the engine has been started, the electric generator is switched from the motor mode to a generator mode in which it is actuated by the engine to generate electric energy, which is supplied to the battery or the propulsive electric motor.
Hybrid vehicles of the type described above are also required to meet demands for environmental protection. However, while the electric generator is being actuated by the engine, the engine emits exhaust gases into the atmosphere. Although toxic emissions harmful to the environments can be reduced from the exhaust gases with a system composed of an exhaust gas sensor, an exhaust gas purifying catalyst, etc. during stable operation of the engine, undesirable harmful emissions tend to be discharged from the engine especially when the engine is started because the fuel combustion in the engine is unstable at the engine start.
Another problem is that when the electric generator is switched from the motor mode to the generator mode, the engine is subjected to load variations. If the load variations are large, then the operation of the engine becomes unstable, causing the engine to vibrate undesirably or emit unwanted harmful exhaust gases.
To supply the generated power from the electric generator to the battery and the propulsive electric motor for extending the range that the vehicle can travel while maintaining necessary vehicle performance factors, the electric generator should preferably be operated frequently.
However, such frequent operation of the electric generator is not desirable from the standpoints of environmental protection and battery life as it requires simultaneous frequent operation of the engine.
For the above reasons, it has been desired to control the hybrid vehicle by starting the electric energy generating apparatus with accurate timing in view of the conditions of the battery and the vehicle driving performance factors, and also by starting the engine and switching between the generator modes under suitable operating conditions in view of the exhaust gas properties and vibration characteristics of the engine.